text: Ray tracing techniques can be applied to study light scattering by spherical and non-spherical particles under the condition that the size of a particle is much larger than the wavelength of light. The light can be considered as collection of separate rays with width of rays much larger than the wavelength but smaller than a particle. Rays hitting the particle undergoes reflection, refraction and diffraction. These rays exit in various directions with different amplitudes and phases. Such ray tracing techniques are used to describe optical phenomena such as rainbow  of halo on hexagonal ice crystals for large particles. 
  Review of several mathematical techniques is provided in series of publications.
  The 46° halo was first explained as being caused by refractions through ice crystals in 1679 by the French physicist Edmé Mariotte (1620–1684) in terms of light refraction  
  Jacobowitz in 1971 was the first to apply the ray-tracing technique to hexagonal ice crystal. Wendling et al. (1979) extended Jacobowitz's work from  hexagonal ice particle with infinite length to finite length and combined Monte Carlo technique to the ray-tracing simulations.